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A.4 Communication System Support
Section A.3 presents example urban, suburban, metropolitan, and rural ITS communication
system designs and cost estimates to procure and install communication systems. This section
win present methodologies to estimate the costs to operate the communication system and
calculate the life cycle costs (LCC). Example L~CC estimates are presented Hat illustrate typical
trade-offs encounters in ITS communication system design.
This section addresses Me following:
.
.
General Overview: Ma~nt~nabiiity of advanced communication systems
Reliability, availability, and maintainability planning and estimating;
Maintenance personal staff planning and es~nadng;
Spare parts planning and estimating;
Test equipment requirements; and
Life cycle cost es~nadng methodologies and examples.
A.4.1 General Overview: Maintainability of Advanced Communication
Systems
A major concern of jurisdictions relating to the deployment of advanced communications
technology is ability to maintain new technology. This issue involves several sub-issues
including:
· Ease of maintenance, a basic issue since it impacts training;
· New gaining of the maintenance staff;
· New test equipment requirements and availability; and
· Spares requirements and associated cost of availability.
To provide a basis for We discussion of maintainability, it is important to understand Mat by
advanced communications technology we mean that which is not in experimental form, has been
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proved by bow laboratory and field testing and has been productized. Produchzation means Mat
We product is fully documented is in production with established manufacturer's product
support. It is furler a technology which is emerging into operational use but which has not been
historically applied to ITS applications on a widespread basis.
HistoncaBy, copper tw~sted-pa~r coax and point-to-po~nt wireless communications have been
applied to llS communications applications. Typically, proprietary communications network
designs were used. Advanced communications technology is considered to be optical, digital
networks, digital wireless, subband wireless, VSAT, and similar products, including advanced
local area networks ~ANs), budges, routers and switches.
Maintainability does not just happen; it must be designed into systems. Elements Mat make
systems maintainable are:
Use of open systems standards wig proven interfaces (bow hardware and software);
Modular design where components are not agony coupled and are easily replaceable;
Built-in test features web real-time tests conducted;
Real-dme fault detection and reposing;
Network management to support remote fault monitoring by Be maintenance organization;
Levels of test (bu~It-in diagnostics) to isolate failures in specific replaceable modules to a
high degree of confidence;
Safe, hot, change-out of failed modules eliminating the need to deactivate power and
reinitialize the system;
Test bus to support use of test equipment; and
Use of fault propagation prevention to contain a fault, preventing Be distribution of
"garbaged" data throughout Be communications network.
Modem communications equipment is evolving to incorporate Be of the Test Architecture and
Bus of Be loins Test Action Group and EKE's Pll49.5. The EKE Pll49.5 Test Bus allows
removable modules to be tested and results reported via a network ~nanagement channel. The
Test Bus supports both a system-level test and a removable module-level test through use of test
equipment, aver Be system level repair has been accomplished.
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Operational circuitry also monitors statistical data errors and reports these errors to a central
network management monitoring function. A trend toward higher bit error rates can provide an
indication of an upcoming failure In electronics or a marginal condition In the physical link.
Modern communications networks typically have unintetruptable power supplies (UPS) which
protect the communications network against over and under voltage conditions. Systems
designed for maintainability include monitoring and reporting of battery conditions and the
over/under voltage condition of prime power. Where a battery backup is used and battery charge
is depleted, well designed systems support graced! shutdown and prewashing via network
management.
Loopback test capability is very beneficial in identifying physical link problems and also in
assessing marginal conditions in signal modulation and demodulation. Bit pattern tests
incorporating loopback can help identify a marginal communications condition in much He same
manner as computer memory tests. Loopback tests are also beneficial in isolating multiplexer
problems.
A.4.~.1 Network Management
Network management includes He hardware 'hooks" and associated software to facilitate
management of a communications network Perhaps one of He most important aspects of
modem commum cations system design is attention to including network management within the
architecture.
Network management generally involves:
· Infrastructure Management:
.
Representation and control of communications infrastructure resources;
· Network Element Management:
~ Individual network element management at the level of hardware and software support;
· Resource Management:
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· Management of physical and logical elements of Me network including topology and
configuration related to end-to-end connectivity;
· Service Management:
.
Management of services supported by He network;
Maintenance Management:
.
Support for performance mon~tonng, fault detection, fault isolation, fault reporting and
control for failure recovery; and
Security Management:
.
Control and monitoring of network secunty.
Network management technology is in a standards evolution phase. Open Systems Institute
(OSI), International Standards Organization DSO), and He Intemational Telecommun~cabons
Union DID) are supporting standards.
ISO/lTU Recommendation X.701; "Open Systems Interconnection System Management
Overview," and
ITU Recommendation M.3000; "Overview of Telecornmun~cadons Management Network
(IMN) Standards."
From these standards efforts, Common Management Formation Services (CMIS) and Common
Management Formation Protocol (CMIP) are emerging. CMIP supports CMIS by transporting
management commands and information from one system (or subsystem) to another.
Simple Network Management Protocol (SNMP) seems to be He current "default" standard in the
communications network industry. Openv~ew (Hewlett Packard, ~c.) Netv~ew (DIM) and
Sunnet (Sunsoft, Inc.) support SNMP. None of the SNMP-supported commercial management
software packages provide a complete system management capability related to maintenance.
fact, evaluations of He Free commercial SNMP software packages rated them:
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Alarm Monitoring:
Alarm Filter~ng/Automation: C
Alarm Correlation:
Ease of Problem Identification: B
Network Topology Viewing: B+
Ability to Identify a Failing Component: A
B
C
SNMP is being improved and wiB most likely converge vv~ ~e CMIP standard.
What is important in die system design process is to assure that ad components of He
communications network support a common network management protocol (whether SUMP or
the final approved standard). Without a common network management protocol supported by
multiplexers, snatches, bridges, routers, etc., complete system-we maintainability Trough
network management is not achievable.
The information network management win provide, when properly implemented, is '~hat has
failed," "where it has failed," and "impact on system performance." This can be extended
Trough applications software to include inventory control of spares, replaceable modules, plus
scheduling and mon~tonng of repair activity.
A4.~.2 Factory Backup
For large communications network subsystems such as SONET node equipment, ATM switches,
bndge-routers, and over tokens equipment is available with a remote diagnostics port. This
port is usually an RS-232 compatible port supported by a Public Telephone Network (PTN)
compatible modem. The communications port can be used by Be manufacturer's maintenance
support services to provide "expert" assistance to a user's maintenance organization in
diagnosing a problem. If equipment win remote diagnostics ports is selected for a system, this
feature provides a second tier maintenance backup to a jurisdictional maintenance organization.
Where many subsystems include factory diagnostics communications ports, these may be
incorporated into a common communications network,~w~ a single point interface to Be PrN at
the Traffic Operations Center (TOC). This reduces the service cost of dial-up circuit access at
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field locations. Typically an overlay RS-232 maintenance circuit would be integrated win the
communications network design. This provides a means of communicating with the failed
network subsystem. Where fault tolerant communications devices are used providing very high
network availability, a multiplexed channel may be dedicated to remote diagnostics support.
The factory maintenance port is usually a higher level maintenance port compared win the
multifunctional network management link which supports failure reporting and maintenance
activities. The factory maintenance port is designed for wide area communications interface
supporting a communications link between equipment and factory maintenance. The port is
further accessible for local, plugger test equnpment and may also be used by field maintenance.
A.4.~.3 Contract Services for Network Management and Equipment
Maintenance Support
Larger networks with a network management protocol and remote diagnostics capability can be
designed wad contract maintenance. To be responsive, He Maintenance Organization must be
within a suitable maintenance response distance from Me communications network. This
typically means Mat Be Maintenance Organization is within Me jurisdictional area
The type of contract service is a function of:
· Use of fault tolerant equipment in Me field;
· Any maintenance responsibility desired to be maintained by He jurisdiction such as:
· Traffic controller maintenance, and
Modem maintenance within traffic controllers;
· Degree of intelligence in the field and ability of He distributed intelligence to safely support
traffic control in case of a communications failure;
· General jurisdicdonal traffic conditions; and
· Responsibility for maintenance service to He electronics and cable infrastructure.
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Where fault tolerance and intelligent distnbuted control are used in a system design, the need for
2=hour per day, 7 days per week monitoring and guaranteed maintenance corrective action
response gene~y is not consider. Monitoring and maintenance are conducted during
stan~d work hours at a cost reduction which can be as much as 50%.
Where failure response time guarantees are included in the maintenance contract, We response
dine period directly relates to service cost. Typically a 2, 4, 6, or 8-hour response time selection
is available with 2-hour response tune costing 30% more Wan S-hour response time. Again, with
fault tolerance in the field, response time is not critical. With fault tolerant systems We
maintenance contract usually guarantees corrective action within the next ~ hour work day
following a failure.
Where a cable infrastructure maintenance contract is in use, typically co~rec~ve action
guarantees and even cost of maintenance action are not included in the contract. Cost of
monitoring, detecting, and isolating a cable break is covered in the connect. The reason for this
is that the maintenance contractor does not know the degree of difficulty associated with
accessing the break, nor the length of time that it will take to access the cable.
A cable break under a Dive or street requires:
Coordination and approval of the junsdiction;
Traffic management and safety considerations;
Concrete (or other surface) penetration;
Conduit location, access penetration; and
Break repay, including restoration of conduit and cable integrity ninth environment (such as
installing a splice closure).
Thus, cable infrastructure repair is typically accomplished on a billable time and materials
contract basis.
With automated built-~n test capability and network management, contract maintenance may not
be justified based on network complexity. With automated fault detection, isolation, and
repordug through a properly designed communications network, the jurisdictional maintenance
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Representative terms from entire chapter:
test equipment
technician is told what is broken, what module(s) to change, and where. Thus, the need for
contract maintenance service is perhaps not justified. For networks Mat do not stress fault
detection, isolation, and fault propagation prevention and reporting, network ~oubleshoodug
becomes a complex task requ~nng detailed knowledge of network hardware and software,
necessitating consideration of contract maintenance support, even with experts providing the
maintenance service, due to We level of maintenance complexity.
Contract maintenance may optionally relieve the jurisdiction of the requirement to purchase
spares. Typically, the contract maintenance organization provides the spares and is responsible
for failed module repair at the component level. While this can save a jurisdiction perhaps 15%
of the cost of con~mun~cadons electronics Hardware only, not including installation and test and
not including cable infrastructure) the disadvantages are:
Funding is usually available to procure required operational spares as part of the initial
system procurement, but maintenance funds are usually more difficult to obtain for He
purpose of purchasing spares after the system has been in operation.
· If the maintenance contact becomes unsatisfactory Cause of poor maintenance
management, spares would have to be procured then, if not initially procured;
· Generally, not all of He equipment in He system is provided by He provider of maintenance
services; therefore, He quality of maintenance service may be degraded; and
.
Generally, it is beneficial for He jurisdiction to have a trained maintenance staff which can
support technical planning for modification and expansion as well as being responsible for
maintaining He system to meet required availability objectives of the junsdiction.
In summary, contract maintenance is available to jurisdictions, wig a savings in personnel, test
equipment, and spares cost. By electing contract maintenance, a jurisdiction becomes vulnerable
to increased maintenance service cost with few alternatives because He maintenance
organizadon owns spares, test equipment, and maintenance knowledge. The better solution is to
use He hardware manufacturers as a backup to jurisdictional maintenance and to repair modules
at He component level, with He jurisdiction purchasing operational spares and integrating
system-level test equipment Into He operational system. Thus, He jur~sdicHon is in control of its
L::U
operations, system availability objectives, and resources for technical planning and growth
support.
A.4.~.4 Impact of Fault Tolerance on Maintainability
Fault tolerance directly impacts system reliability and also impacts maintenance. Through use of
the fault tolerant designs available in advanced communications products, a failure can occur
without ~ntern~pting communications. The network management software reports We occurrence
of We failure and the fact that We backup module has been committed to operation or that a
counter-rotat~ng optical nag is operating in a failure infonnation routing mode. Maintenance can
be scheduled, bred on optimized use of maintenance resources. Thus, crisis maintenance is
eliminated.
Where large distributed systems are involved, use of fault tolerance can be justified based on
maintenance cost savings. Group more efficient use of maintenance time, the system can be
mainlined with fewer repair personnel and fewer trips to the field.
Un~nterruptable Power Supplies (UPS) also reduce maintenance costs and can be justified.
Powering on and off electronics induces the highest stress on semiconductors, which results in
failures. By eliminating power cycling during loss of prime power, failures of electronic
equipment are reduced. Maintenance time to restart He system and synchronize databases after
a power failure is also eliminated.
A.4.~.5 Reliability of Advanced Communications Technology as Related to
Maintainability
Older communications equipment used discrete components, each having a discrete failure rate.
Advance communications equipment typically uses highly integrated circuitry which supports
reduced component count Similarly, advanced communications equipment typically uses low
power semiconductor components with low heat dissipation, unlike older technology. Lower
power and heat dissipation supports higher reliability since semiconductor failure rate increases
with junction temperature.
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New integrated circuits are being designed wig test interfaces that integrate with board level test
buses. Thus, maintainability at He system, board, and chip levels is enhanced.
A Bird trend, use of Digital Signal Processors (DSP) to perform communications functions, is
also improving advanced communications reliability and further supports maintainability. The
results are fewer components, intelligence to support self diagnostics, and generally more
communications functionality.
Use of DSPs, Programmable Logic Arrays (PLAs), Applications Specific Integrated Circuits
(ASIC) and other large-scale integration techniques in modern communications:
Reduces component count;
· Reduces mechanical connections; and
.
Reduces problems protecting circuitry against noise (coupled and caused by ground planes).
Thus, reliability of Me communications device is increased. This, combined w~ff1 the ability to
Impose built-in testing down to the component level, the need for maintenance operations for
advanced communications devices is decreased, and the ease of conducting a maintenance
operation when needed is increased.
A.4.~.6 Built-in Test Equipment
As opposed to built-in tests, which are test features incorporated into the design of operational
communications electronic equipments, test equipment may be integrated into the system. Test
equipment supplements those devices which do not have built-~n tests or are incapable of
~nco~poradog built-in test features. A fiber cable, for instance, requires special test equipment to
determine We location of a broken connection.
Prudent system design integrates test equipment wig the operational system using test data
buses, switches, and patch panel capability. Integrating test equipment wig the operational
system has He following benefits:
.
Easy access and use for testing;
L.\NC~RP\~.spt\ NCHRP 3-51 · Phase 2 Fmal Report
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· Availability when needed (not in the back of a maintenance van out in the field);
· Highly complimentary to bu~It-in test features of Be system; and it
· Can be budgeted and justified as part of the operational system.
Test equipment supporting advanced communications technology is being designed to be:
Compatible wad recognized test bus standards;
Able to be integrated into a common system test capability;
Able to be controlled and test results read by system bu~It-in test software supporting central
network management capability; and
Generally modularly expandable and tailorable Trough software (example is protocol
analyzer).
Thus, it is prudent to incorporate test equipment in Me system design as needed to fib the test
gaps.
A.4.~.7 Jurisdictional Maintenance Skills and Compatibility with Advanced
Communications Technology
There is no question Hat advanced communications technology is more complex Han
conventional technology; however, complexity and understandability are not Incompatible In
advanced systems. There are many reasons for this including:
· High degree of functional integration places complexity below the replaceable module level,
making it only necessary to understand the higher level function at Be module level;
· Use of built-in test (Brie), fault isolation, and fault reporting. Requirements for detailed
analysis of bit patterns, voltages, and waveforms are minimized because the '~IT' report
defines He problem and its location;
° Advanced communications use self calibration m~nuniz~ng the need to manually adjust
circuit parameters. The trend is approaching total automatic adjustment, even for radio
frequency commun~cabons equipment;
~WCHR~se2~t\ NCHRP3-51 · Phase2FmalReport
Af11
· Automated module test sets and electronic modules with test buses support automated
component failure isolation. Maintenance sums needed relate to how to use the removable
module test set and how to change large-scale integration components. ~ addition, many
manufacturers offer board-level repair service as an option;
· Use of bus standards at module and system levels means basic standards are He same for
signals and control protocols between equipment (OST layers ~ and 2~.
.
Use of the same standard link and network protocols and network management standards
between network elements; and
Emphasis on ergonomics In systems operation and maintenance simplifies understanding of
system '~ealth.~,
With advanced communications, when systems are properly designed, troubleshooting is
automated and maintenance is generally accomplished at a higher level of understanding (more
low-level functions are bundled together to provide a higher level function). Standards are used
for interfaces and ergonomics are considers in presentation of bu~It-in test results to
maintenance personnel. Emphasis on braining is at Be subsystem and systems level wig less
emphasis on module-level maintenance.
Because of their fi~ncdonal understanding and basic communication knowledge, jurisdictional
maintenance personnel are generally capable of making Be transition from conventional to
advanced communications support Generally, maintenance personnel Avid support Be
opportunity to move forward wig technology, as long as they are provided the 'fools" to
accomplish progress. This means that Be system is supplied ninth modern BIT features and
integrated test equipment to support maintenance operations and that cen~ized
communications network management and monitoring are included In the system. Without
attention to automated maintenance assistance in new systems, jurisdictional maintenance
support for advanced technology implementation we most likely be limited. The task of
troubleshooting and maintaining a complex system, without BIT and control maintenance
monitoring features, would be difficult even wig trained maintenance personnel.
L;`NCHRPPhase~p ~NCHRP 3-51 · Phase 2 Fm~1 Report
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The transition from copper infrastructure to wireless infrastructure has proved easily
accommodatable by jurisdictional maintenance personnel. Communications principles apply,
such as signal attenuation loss versus distance, and ban~vv~ as a function of distance.
Concepts of frequency multiplexing apply in He sense of wave division multiplexing. Cables are
color coded in Be standard manner. The difference is in configuration, splicing, and test
equipment to measure parameters. With automated splicing tools which splice and verify the
connection bow mechanically and opthcally, splicing of optical cable is simplified.
For a cable comn~un~cabons maintenance technician to become a wireless technician requires
training; however, Be transition of a jurisdictional mobile radio maintenance technician to
support a modern digital wireless communications network is achievable without major
difficulty. The reason is Mat Be basic theory of wireless communications is already understood
by Be maintenance technician. Thus, the functions of the advanced wireless digital transceiver
and associated BIT are more easily understood as an extension of current knowledge.
In summary, wad a basic knowledge of communications technology, advanced commun~cabons
applying communications principles, built-in test features, and central network monitoring, a
jurisdictional maintenance technician is capable of transition~ng from conventional to advanced
communications network maintenance.
A.4.~.S Software Maintainability
In communications equipment employing software, software ma~ntainabilit~,r is a concern. Older
communications equipment did not employ structured, modular software developed under
recognized procedures for quality software products.
The Institute of Electrical and Electronic Engineers (' ~ ~E) has prepamcl standards for software
development, documentation, and testing. LIFE Standard 1219-1992, entitled "Standard for
Software Maintenance" applies. EKE document 89-1983, entitled "Measures to Produce
Reliable Software" and WEE Standard 10008-1987, entitled "Standard for Software Unit
Testing" are important in achieving software maintainability. Attention to software
documentation as defined in ISLE Standard 1063-1987 (Software User Documentation) and
101~1993 (Guide to Software Design Description) furler supports software maintainability.
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